Fig. 4.

Quantitation of the effects of prephosphorylation of tau by PKA on the subsequent phosphorylation at individual sites by cdk5/p25. Tau₄₄₁ (Tau) and PKA-phosphorylated tau₄₄₁ (P-tau) (0.2 mg/ml) were incubated with cdk5/p25 for various periods of time, and the phosphorylation level of tau at each individual site was determined by using an immuno-dot-blot assay developed with phosphorylation-dependent and site-specific tau antibodies, as indicated in each panel. All the data had been normalized with the amounts of tau protein, as determined by using phosphorylation-independent tau antibody R134d.